It goes without saying that every conscientious canner will select only prime vegetables or fruit; prepare them carefully; pack them and pressure-process them correctly; check seals; and store in a cool, dark, dry place 24 hours after they've been canned.
There are many little hints about canning that can make the job easier and explain some of the techniques used. Here are some of the questions that often come up, with some answers.
Q What causes jelly to be too soft?
Too much juice in the mixture, too little sugar, mixture not being acidic enough for overripe fruit, or making too big a batch at one time.
Q Is it safe to can foods without salt?
Yes. Salt is used for flavor only in canned vegetables and is not necessary for safe processing. Since the flavor and texture of pickled vegetables depend on salt, don't omit it from recipes for pickles and relishes.
Q What causes canned foods to change color?
Discolored food is OK to eat, although not attractive. Darkening of food at the top of the jar is caused by oxidization due to air in the jar, or it may be caused by too little heating or processing so that enzymes are not destroyed.
Overprocessing may also cause discoloration.
Pink and blue colors often seen in jars of pears, apples, and peaches are caused by chemical changes in the fruit coloring matter.
Q Why does fruit sometimes float after canning?
Fruit may float because it is packed too loosely, because the syrup is too heavy, or because some air remains in tissues of the fruit after heating and processing.
Q Why is headroom important in canning?
It allows for expansion of solids or bubbling up of liquid during processing. If head space is not adequate, some food in the container will be forced out.
When too much head space is allowed, some air may remain in the jar after processing, causing food at the top to darken.
Q Why is oven canning unsafe?
Jars may explode, causing damage to both the cook and the oven. Also, temperatures in the home oven are not high enough to ensure adequate destruction of spoilage organisms in low-acid foods.
Q What can you do if the jelly doesn't jell?
Use it as a topping for pancakes, ice cream, or other desserts. You may also try recooking the mixture.
Q Why do some vegetables need more headroom than others?
Starchy vegetables swell during processing, especially if they're packed raw, so they need double the headroom of nonstarchy foods. Be especially careful about shell beans of all kinds, green peas, and whole-kernel corn.
Q How do you know when to use or not use water from blanching vegetables?
Some vegetable water can be bitter, depending on how hard the water is. Water from asparagus or the turnip family when precooked for hot pack can be bitter. Taste the water, and if it is too strong or slightly bitter, discard it and use plain water.